On 2.08.2018 13:09, Anand Jain wrote:
> When the replace is running the fs_devices::num_devices also includes
> the replace device, however in some operations like device delete and
> balance it needs the actual num_devices without the repalce devices, so
> now the function btrfs_num_devices() just provides that.
>
> And here is a scenario how balance and repalce items could co-exist.
> Consider balance is started and paused, now start the replace
> followed by a power-recycle of the system. During following mount,
> the open_ctree() first restarts the balance so it must check for the
> replace device otherwise our num_devices calculation will be wrong.
>
> Signed-off-by: Anand Jain <anand.j...@oracle.com>
> ---
> v2->v3: update changelog with not so obvious balance and repalce
> co-existance secnario
> v1->v2: add comments
>
> fs/btrfs/volumes.c | 32 ++++++++++++++++++--------------
> 1 file changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index fe74fefc75f7..8844904f9009 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1854,6 +1854,21 @@ void btrfs_assign_next_active_device(struct
> btrfs_device *device,
> fs_info->fs_devices->latest_bdev = next_device->bdev;
> }
>
> +/* Returns btrfs_fs_devices::num_devices excluding replace device if any */
> +static inline u64 btrfs_num_devices(struct btrfs_fs_info *fs_info)
> +{
> + u64 num_devices = fs_info->fs_devices->num_devices;
> +
> + btrfs_dev_replace_read_lock(&fs_info->dev_replace);
> + if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
> + BUG_ON(num_devices < 1);
> + num_devices--;
> + }
> + btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
> +
> + return num_devices;
> +}
> +
> int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
> u64 devid)
> {
> @@ -1865,13 +1880,7 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info,
> const char *device_path,
>
> mutex_lock(&uuid_mutex);
>
> - num_devices = fs_devices->num_devices;
> - btrfs_dev_replace_read_lock(&fs_info->dev_replace);
> - if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
> - BUG_ON(num_devices < 1);
> - num_devices--;
> - }
> - btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
> + num_devices = btrfs_num_devices(fs_info);
How about lifting the BUG_ON from btrfs_num_devices into a check in this
function, so if num_devices < 1 then we just exit with -EINVAL or some
such. We should be aiming at eliminating BUG_ONs.
>
> ret = btrfs_check_raid_min_devices(fs_info, num_devices - 1);
> if (ret)
> @@ -3721,13 +3730,8 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
> }
> }
>
> - num_devices = fs_info->fs_devices->num_devices;
> - btrfs_dev_replace_read_lock(&fs_info->dev_replace);
> - if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
> - BUG_ON(num_devices < 1);
> - num_devices--;
> - }
> - btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
> + num_devices = btrfs_num_devices(fs_info);
> +
> allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE | BTRFS_BLOCK_GROUP_DUP;
> if (num_devices > 1)
> allowed |= (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID1);
>
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